Improved tool for cutting screw-threads



,Staten Griffin.

Mem by 'nteutl ELIJAH S. PIERCE, OF HARTFORD, CONNECTICUT, ASSIG-NOR TOv .THE NATIONAL SCREW COMPANY, OF SAME PLACE.

Lette/rs Patent No. 87,198, (lated February 23, 1869.

IMPROVBD TOOL FOR CUTTING SCREW-THREADS.

The Schedule referred to in these Letters Patent and making part of lthe same.

To all whom it may concern.-

Be it known that I, ELIJAH S.P1EncE, of Hartford, in the county of Hartford, and State of Connecticut, have invented certain new and useful Improvements in Tools for Cutting Screws; and I dol hereby declare that the following is a full,'clear, and exact description thercof, whereby a person skilled in the art can make and use the same, reference being had to the accompanying drawings, andto the letters of reference marked thereon.

Like.- letters in the figures indicate the same parts.

Figure l is'a hack view of my improved tool.

Figure 2 is a side View.

Figure 3 is a front view, and

Figure 4 is a cross-section of the same.

Figure 5 is a longitudinal section of a screw, on an enlarged scale, ont by my improved tool.

Figure 6 shows a horizontal section of the screw, and the position of the tool while cutting the thread.

My invention consists in a tool which has twoinclined cutting-edges for forming the bottom of the groove between the threads, so as to give the endscf the-core', atthe-commencement of the thread and at the point of the screw, a conical form, and the intermediate part, the form of a low supplemental thread between the convolutions of the principal thread, shown in iig. 5.

The tool is a straight steel bar, of the cross-section shown in 1i 4, having its extremity e ground oit' to the proper angle, back from the edges a and b, to form a cutting-tool, and to such lateral angle that, when the tool is in use, and held to the blank in a direction corresponding to the pitch ofthe thread, the plane of the said extremity shall lie parallel to the longitudinal axis of the blank.

The sides of the groove c and the outside edges d d form the thread, and the edges a and b, the bottom of the groove. The tool is held to the blank in such position that the directionA of the groove c shall correspond to the direction or pitch of the thread, afiidis moved forward against and'laterally along the screw-blank in the manner usual in screw-cutting and threading machines.

XVhen the tool tirst enters the screw at m, tig. 5, the edges a and b commence to cut, anda, following b, forms theconical part of the core to n, or so long as the tool is advanced toward the axis of the screw, after which the edge, b, also cuts part of the bottom of the groove, and the two finish the central core from a to o, in the form shown in tig. 5.

From o to 11, the tool is again advanced, and the edge, a, finishes the conical portion of the core.'

The advantages of my invention are that it cuts a screw with a conical point to the core, and a supplemental thread along the cylindrical portion In o, whereby the screw is made to enter more easily and hold more firmly than' when the bottom of the groove is of a volute. 

